I can only think in something like a runbook in Azure Automation, triggered with something like an item list with the properties for the SC creation and a flag column (Create yes/no). The runbook would read the item, and if Create is "yes" it would take the properties for site creation (checking URL doesn't exist, etc etc). Something like this, if you want to play:

https://www.stadlersoftware.com/powershell/sharepoint-online-with-azure-runbooks/

The runbook would store and use admin credentials

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